Advertisements
Advertisements
Question
There are 25 rows of seats in an auditorium. The first row is of 20 seats, the second of 22 seats, the third of 24 seats, and so on. How many chairs are there in the 21st row ?
Advertisements
Solution
The arrangement of chairs is 20, 22, 24, 26, ..........
Which is an A. P.
Here, a = 20, d = 2. We want to find t21.
tn = a + (n-1)d
∴ t21 = 20 + (21-1) × 2
= 20 + 40
= 60
∴ There are 60 chairs in the 21st row.
APPEARS IN
RELATED QUESTIONS
Find the sum of first 30 terms of an A.P. whose second term is 2 and seventh term is 22
If the sum of the first n terms of an AP is 4n − n2, what is the first term (that is, S1)? What is the sum of the first two terms? What is the second term? Similarly, find the 3rd, the 10th, and the nth terms.
Find the sum of the following arithmetic progressions
`(x - y)^2,(x^2 + y^2), (x + y)^2,.... to n term`
Find the sum of the first 15 terms of each of the following sequences having the nth term as
yn = 9 − 5n
Find the sum of the first 22 terms of the A.P. : 8, 3, –2, ………
Is -150 a term of the AP 11, 8, 5, 2, ……?
In a flower bed, there are 43 rose plants in the first row, 41 in second, 39 in the third, and so on. There are 11 rose plants in the last row. How many rows are there in the flower bed?
The first term of an AP is p and its common difference is q. Find its 10th term.
How many terms of the AP 21, 18, 15, … must be added to get the sum 0?
Find the first term and common difference for the A.P.
127, 135, 143, 151,...
The sum of third and seventh term of an A. P. is 6 and their product is 8. Find the first term and the common difference of the A. P.
A man is employed to count Rs 10710. He counts at the rate of Rs 180 per minute for half an hour. After this he counts at the rate of Rs 3 less every minute than the preceding minute. Find the time taken by him to count the entire amount.
If Sn denote the sum of the first n terms of an A.P. If S2n = 3Sn, then S3n : Sn is equal to
The sum of n terms of an A.P. is 3n2 + 5n, then 164 is its
If the second term and the fourth term of an A.P. are 12 and 20 respectively, then find the sum of first 25 terms:
The 11th term and the 21st term of an A.P are 16 and 29 respectively, then find the first term, common difference and the 34th term.
Find S10 if a = 6 and d = 3
The sum of first 16 terms of the AP: 10, 6, 2,... is ______.
An AP consists of 37 terms. The sum of the three middle most terms is 225 and the sum of the last three is 429. Find the AP.
In an AP, if Sn = n(4n + 1), find the AP.
